UMD Astronomer Co-Leads Creation of First 3D Temperature Map of Distant Exoplanet

This new technique lays the groundwork for more detailed future explorations of faraway planets.

Astronomers have generated the first three-dimensional map of a planet orbiting another star, revealing an atmosphere with distinct temperature zones—one so scorching that it breaks down water vapor, according to a new paper published in the journal Nature Astronomy on October 28, 2025.

Co-led by the University of Maryland and Cornell University, the research details the team’s effort to create a temperature map of WASP-18b—a gas giant known as an “ultra-hot Jupiter,” located 400 light-years from Earth. The group’s map is the first to apply a technique called 3D eclipse mapping, also known as spectroscopic eclipse mapping. This study builds on a 2D model that members of the same team published in 2023, which demonstrated eclipse mapping’s potential to tap into highly sensitive observations by NASA’s James Webb Space Telescope (JWST).

“This technique is really the only one that can probe all three dimensions at once: latitude, longitude and altitude,” said the paper’s co-lead author Megan Weiner Mansfield, an assistant professor of astronomy at UMD. “This gives us a higher level of detail than we’ve ever had to study these celestial bodies.”

Using this technique, the researchers say they can now begin mapping atmospheric variations for many similar types of exoplanets observable by JWST, just as Earth-based telescopes long ago observed Jupiter’s Great Red Spot and banded cloud structure.

“Eclipse mapping allows us to image exoplanets that we can’t see directly, because their host stars are too bright,” said the paper’s co-lead author Ryan Challener, a postdoctoral associate in Cornell University’s Department of Astronomy. “With this telescope and this new technique, we can start to understand exoplanets along the same lines as our solar system neighbors.”

Detecting exoplanets has always been difficult—they typically emit much less than 1% of a host star's brightness. Eclipse mapping involves measuring small fractions of that total as a planet circles behind its star, obscuring and revealing parts of it along the way. Scientists can link minute changes in light to an exoplanet’s specific regions to produce a brightness map that, when rendered in multiple colors, can map out temperatures in latitude, longitude and altitude.

WASP-18b, which has roughly the mass of 10 Jupiters, orbits in just 23 hours and has temperatures approaching 5,000 degrees Fahrenheit—providing a relatively strong signal that made it a good test case for the new mapping technique.

While the team’s earlier 2D map of WASP-18b utilized a single light wavelength, or color, the new 3D map reanalyzed the same observations from JWST’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument in many wavelengths. Each color on the map corresponded to different temperatures and altitudes within WASP-18b’s gaseous atmosphere, which could then be pieced together to create the new, more detailed three-dimensional map. 

“If you build a map at a wavelength that water absorbs, you’ll see the water deck in the atmosphere, whereas a wavelength that water does not absorb will probe deeper,” Challener explained. “If you put those together, you can get a 3D map of the temperatures in this atmosphere.” 

The new 3D view confirmed spectroscopically distinct regions—differing in temperature and possibly in chemical composition—in WASP-18b's visible “dayside,” the side that always faces the star due to its tidally locked orbit. The planet features a circular “hot spot” where the most direct starlight lands and where winds apparently aren't strong enough to redistribute the heat. Surrounding the hot spot is a colder “ring” nearer the planet's outer visible edges, or limbs. Notably, measurements showed lower levels of water vapor in the hot spot than WASP-18b's average.

“We’ve seen this happen on a population level, where you can see a cooler planet that has water and then a hotter planet that doesn’t have water,” Weiner Mansfield explained. “But this is the first time we’ve seen this be broken across one planet instead. It’s one atmosphere, but we see cooler regions that have water and hotter regions where the water’s being broken apart. That had been predicted by theory, but it's really exciting to actually see this with real observations.”

Researchers believe that additional JWST observations could help improve the spatial resolution of this first 3D eclipse map. Weiner Mansfield noted that the technique has opened up many new avenues of research for similar “hot Jupiters,” which make up hundreds of the more than 6,000 exoplanets confirmed to date. In the future, she also hopes to apply 3D eclipse mapping to smaller, rocky planets beyond hot, gassy planets like WASP-18b 

“It’s very exciting to finally have the tools to see and map out the temperatures of a different planet in this much detail. It’s set us up to possibly use the technique on other types of exoplanets. For example, if a planet doesn’t have an atmosphere, we can still use the technique to map the temperature of the surface itself to possibly understand its composition,” Mansfield said. “Although WASP-18b was more predictable, I believe we will have the chance to see things that we could never have expected before.” 

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This article was adapted from text provided by Cornell University.

The paper, “Horizontal and Vertical Exoplanet Thermal Structure from a JWST Spectroscopic Eclipse Map,” was published in Nature Astronomy on October 28, 2025. 

This research was supported by the James Webb Space Telescope’s Transiting Exoplanet Community Early Release Science Program.